In order to increase the cutting speed of machine tools such as machining centers, a high rotational speed is desired for spindles which transmit rotational force to a tool while the tool is held in place. To achieve a high spindle rotational speed requires consideration of items such as lubrication or cooling of the bearing and the dynamic balance of rotating portions, including the spindle. In addition, it is important to increase the static rigidity and fhe dynamic rigidity of the spindle, and to reduce its thermal deformation and inertial force.
In general, all or most parts of the spindle are made of carbon steel or steel alloys. Rapid acceleration and rapid deceleration of high specific gravity steel spindles is limited by large inertial force. Therefore, in order to reduce inertial force, it is desirable to reduce the specific gravity of the spindle with out sacrificing strength.
Machine tool spindles are known in which a ceramic cylindrical body having a tapered inner surface which clamps a tool holder is joined to a steel spindle body. However, the bonding between two parts of differing coefficients of expansion may loosen.